The invention relates to adhesive articles and the production thereof.
Adhesive tape comes in many varieties; for example, transfer tape, single-sided tape, and double-sided tape. The adhesive tape can be a foamed or non-foamed tape. Double-sided adhesive tape has adhesive properties on both sides. The macro-structure and method of producing standard double-sided adhesive tape is relatively simple and one method of production and the resulting structure is as follows. The adhesive polymer that is to make up the actual adhesive tape is readied and extruded by some acceptable method. Next, the adhesive polymer is immediately combined with a liner. Suitable liners for double-sided adhesive tapes include backings that have been coated on both sides with a release coating. The liner and the adhesive polymer are then laminated to form the double-sided adhesive tape product.
In high performance adhesive tapes, typically the next step is to crosslink the adhesive polymer. It is generally advisable to crosslink the adhesive polymer because it imparts desirable properties to the final product, such as improving the cohesive strength of the adhesive. Crosslinking can be accomplished by exposing the adhesive polymer to radiation (e.g., electron beam, ion beam or ultraviolet radiation). The double-sided adhesive tape product is then wound into a roll so that both surfaces of the double-sided adhesive tape are covered with a liner, the first surface already being covered with a liner because of the method of production, and the second surface of the adhesive tape being covered with the side of the liner that was not covered with the adhesive polymer initially. Double-sided adhesive tape produced in this manner is designed to have a differential release liner, so that when the tape is unwound, the liner remains on the xe2x80x9cright sidexe2x80x9d of the adhesive tape. Liner release is the force required to remove a liner from the adhesive on a tape.
Production of double-sided adhesive tape by this method is desirable, but significant problems are encountered when electron beam (xe2x80x9cE-Beamxe2x80x9d) radiation is used to crosslink the adhesive polymer. E-Beam radiation is advantageous as a method of crosslinking because it is effective to crosslink adhesive polymers that have high amounts of pigments or fillers, and/or adhesive films of greater thicknesses. If the adhesive polymer is exposed to E-Beam radiation (xe2x80x9cE-Beam treatedxe2x80x9d) through the non-liner side (before winding), the adhesive properties of the adhesive polymer itself are altered. For example, a 6 Megarads (Mrads) E-Beam dose may cause the adhesion on the E-Beam treated side of an acrylic adhesive polymer to be diminished 30 to 50%. In order to maintain an acceptable level of adhesion on both sides of the double-sided adhesive tape, the adhesive polymer must be E-Beam treated through the liner side.
The surface chemistry of silicone-coated liners traditionally used in double-sided adhesive tape is also altered when E-Beam treated. When the adhesive polymer is E-Beam treated through the liner, the liner release of the side of the liner contacting the adhesive polymer is only slightly increased. In contrast, the liner release on the other side of the liner, i.e., the non-adhesive side treated with E-Beam, is greatly increased. This increase in liner release is detrimental because the non-adhesive side of the liner comes in contact with the adhesive polymer once it is wound into its final product roll. This creates an undesirable situation in the final product wherein the liner is removed from the xe2x80x9cright sidexe2x80x9d of the adhesive tape before the xe2x80x9cwrong sidexe2x80x9d. This is known as xe2x80x9cliner confusionxe2x80x9d. In some cases, the liner cannot even be removed. This is known as xe2x80x9cliner blockingxe2x80x9d. Even when the adhesive is E-Beam treated directly (i.e., not through the liner), the side of the liner opposite the adhesive will be affected if the radiation penetrates through the liner.
One solution to this problem has been to manufacture the double-sided adhesive tape on a temporary liner, crosslink the adhesive with E-Beam radiation, and then replace the temporary liner with another liner before it is packaged into the final product. However, this solution is unacceptable because it adds to the complexity of the process, increases waste of the process, and adds the additional cost of another liner. Therefore, there is a need for a liner that can be E-Beam treated while still maintaining essentially the same pre-E-Beam treated release characteristics so that it need not be replaced before the consumer can utilize the final product.
The invention offers adhesive articles and methods of producing the articles. The adhesive articles of the invention include a liner having a first side and a second side, and an adhesive having a first surface and a second surface, wherein the second surface of the adhesive contacts the first side of the liner, wherein the article has been exposed to E-Beam radiation through the second side of the liner, and wherein the article has been wound upon itself causing the second side of the liner to come into contact with the first surface of the adhesive and wherein the liner release of the second side of the liner to the first surface of the adhesive is sufficiently different (different enough to avoid liner confusion) from the liner release value of the first side of the liner to the second surface of the adhesive. Generally, the liner release value of the second side of the liner to the first surface of the adhesive is less than 280 g/in (110 g/cm). Preferably, the liner release value of the second side of the liner to the first surface of the adhesive is less than 150 g/in (59 g/cm), and most preferably is less than 100 g/in (39 g/cm), e.g., less than 50 g/in (20 g/cm), or less than 30 g/in (12 g/cm).
The invention also includes a method of producing adhesive articles, including the steps of applying release coating material(s) to a second side, and optionally to a first side, of a liner backing, applying an adhesive onto a first side of said coated liner backing; crosslinking said adhesive with E-Beam radiation applied through the second side of said coated liner backing; and winding said article into a roll. Preferably, the release coating material for the liner backing comprises at least one material chosen from the group consisting of: alkoxysilane silicones, acetoxysilane silicones, silanol silicones, epoxy silicones, and vinyl silicones, and preferably comprises silanol-terminated silicones.